Bowser is the leader and most powerful of the Turtle-like Koopa race and is Mario's greedy archnemesis beginning with his first appearance, in the game Super Mario Bros. His ultimate goals are to marry Princess Peach, defeat Mario, and conquer the Mushroom Kingdom. Since his debut, he has appeared in almost every Mario series game.

Bowser is portrayed as the "King of the Koopas", anthropomorphic turtles that inhabit the Mushroom Kingdom. Bowser differs greatly from the rest of his clan, who appear mainly as bipedal tortoises. He has a large, spiked shell, horns, and a shock of red hair. Bowser is physically powerful, can breathe fire, and is said to have skills in black magic.

Bowser aspires to take over the Mushroom Kingdom and merge it with his own hellish world, Dark Land. He is infatuated with Princess Peach,[12][13][14] and routinely kidnaps her as part of his plans for domination. Sometimes, however, he kidnaps Peach to simply lure Mario into a trap.

The character's role in the series varies. He is typically the main villain of the story, but in the RPG series he sometimes works with the heroes to defeat a greater evil.[15] The RPGs also portray Bowser in a more humorous light as a blustering bully with a hidden softer side.

Bowser's first appearance was in Super Mario Bros. as the main villain who kidnaps Princess Peach and as the final boss with several false versions of him appearing as lesser bosses. He reappears in Super Mario Bros.: The Lost Levels, which uses the same battle style. He appears in Super Mario Bros. 3, and along with his seven children, the Koopalings, he transforms the kings of seven worlds into various different creatures and eventually capturing Princess Peach yet again. Bowser and his seven underlings reappear in Super Mario World, where they conquer Dinosaur Land and kidnap Peach while she and Mario are on vacation on Yoshi's Island. He makes his first 3D appearance in Super Mario 64, where he takes over Peach's castle and steals 105 of the 120 Power Stars, scattering them through various worlds linked using the castle. He returns in Super Mario Sunshine, in which his youngest son, Bowser Jr., who is disguised as an evil version of Mario, kidnaps Peach. Bowser himself eventually appears in the final boss battle of the game. In New Super Mario Bros., Bowser is the boss of the first world, which features a battle similar to that of Super Mario Bros. After being defeated, he falls into lava and transforms into a skeletal version of himself known as Dry Bowser. He is eventually restored by Bowser Jr. and acts as the final world's boss along with his son. In Super Mario Galaxy, Bowser steals Power Stars from Rosalina's Comet Observatory and kidnaps Peach, taking her to the center of the universe to recreate it, with the intention of taking over the universe. He also appears in New Super Mario Bros. Wii as the final boss and primary antagonist of the game. Bowser appears in the sequel Super Mario Galaxy 2, once again as the main villain. Here, however, Bowser has grown to giant size, requiring the player to dodge more powerful attacks such as meteors and electricity bolts.

Bowser appears as a child in various games. Known as Baby Bowser, he antagonizes the Baby Mario brothers and various members of the Yoshi species. He first appears in Super Mario World 2: Yoshi's Island where Kamek predicts the brothers will become problems in the future, so he attempts to kidnap them. He appears yet again in the sequel Yoshi's Story, stealing the "Super Happy Tree" from a group of Yoshis. He appeared yet again in Yoshi's Island DS as a playable character to recover his castle. He made an appearance in the Mario role-playing game Mario & Luigi: Partners in Time as an antagonist.